Dynamic network and routing method for a dynamic network

ABSTRACT

The invention relates to a dynamic network with a plurality of nodes, in which it is provided that—routing information is stored in local routing tables in nodes of the network, —the nodes send an update request to other nodes for updating the local routing tables, and—the addressed nodes send an update response with updated routing information to the requesting nodes.

[0001] The invention relates to a dynamic network and to a routingmethod for a dynamic network.

[0002] A dynamic network is understood to be a network whose topologycan change dynamically during operation. This includes in particular adhoc networks. An ad hoc network is understood to be a self-organizingnetwork in which the structure and the number of participants is notlaid down within given limit values. For example, a communication deviceof a participant may be taken from the network or included in thenetwork. In contrast to traditional mobile telephone networks, an ad hocnetwork is not based on a fixedly installed infrastructure.

[0003] Dynamic networks, however, may alternatively be, for example,Internet networks whose topology changes during operation.

[0004] Such an ad hoc network is known from the book: C. E. Perkins, AdHoc Networking, Addison Wesley, pp. 53-62. Each node in this knownnetwork sends updates of the routing information to adjoining nodes atregular intervals so as to adapt the routing to changes in the networktopology.

[0005] It is an object of the invention to provide a network of the kindmentioned in the opening paragraph which renders possible an improvedrouting in the case of changes in the network topology. It is a furtherobject of the invention to indicate a relevant routing method.

[0006] As regards the network, the object is achieved by means of adynamic network with a plurality of nodes, in which it is provided that

[0007] routing information is stored in local routing tables in nodes ofthe network,

[0008] the nodes send an update request to other nodes for updating thelocal routing tables, and

[0009] the addressed nodes send an update response with updated routinginformation to the requesting nodes.

[0010] In the network according to the invention, routing information isstored in nodes of the network. Routing information is preferably storedin every node in the case of decentralized networks. Routing informationis preferably stored in the central nodes only in the case of clusternetworks with central controllers.

[0011] The routing information is stored in the form of routing tables.The routing table of a node preferably comprises fields for all othernodes of the network or for those nodes which are accessible from thenode in question. The nodes accessible from a given node, i.e. to whicha transmission is possible or desired, are denoted target nodes.

[0012] The routing information stored in the fields, for example of thenext node via which a data transmission to the respective target node isto take place (next hop), may be the path length to the target node andthe maximum transmission capacity to the target node.

[0013] To keep the local routing tables up to date, the nodes having arouting table preferably send an update request to other nodes atregular intervals. These other nodes are in particular adjoining nodes.They are in particular adjoining controllers in the case of clusternetworks with central controllers.

[0014] The update request signals to the nodes receiving this requestthat they should send updated routing information to the requestingnodes.

[0015] The advantage of the requesting mechanism is in particular thatthe requesting mechanism renders possible a combined transmission of therouting information. The individual nodes transmit modified routinginformation upon request only. In the case of a request, severaltopology changes, i.e. the topology changes that have occurred in thetime period between two requests, may then be sent jointly to therequesting nodes. In a single protocol data unit (PDU), accordingly,several changes in the network topology can be sent to the requestingnodes. This leads to a reduction in the number of PDUs (packets) whichare to be transmitted for the routing purposes.

[0016] The invention is based on the idea that the quantity of data tobe transmitted for updating the local routing tables can be reduced inthat the individual nodes request routing information from other nodes.

[0017] The advantageous embodiment of the invention as defined in claim2 is based on the idea that it is notified to the addressed nodes how upto date the routing information of the requesting nodes is. This rendersit possible for the addressed nodes to make a selection of routinginformation which is to be sent to the requesting node. Only thoserouting data are transmitted to the requesting node each time which aremore recent than the routing information of the requesting node up tothat moment.

[0018] For this purpose, the local routing tables contain a table updateinformation and a field update information. The table update informationcontains data on how up to date the local routing table is, i.e. whenthe latest change in the routing table was applied. This may be, forexample, a time indicator or a sequence number. The field updateinformation contains data on how up to date the individual fields of therouting table are, i.e. when the latest change was applied in therespective field of the routing table. The field update information mayagain be, for example, a time indicator or a sequence number. The tableupdate information thus corresponds to the most recent field updateinformation of the respective routing table.

[0019] The update request contains the table update information of therequesting node. This allows the addressed node to make a selection ofthe routing information to be sent to the requesting node. The addressednodes know from the table update information of the requesting node howup to date the routing table of the requesting node is, i.e. when themost recent change was made in the routing table of the requesting node.The addressed nodes send an update response containing only that localrouting information which is more recent than the table updateinformation to the requesting node. If the table update information is atime indicator, only those routing data are transmitted which are morerecent in time. The selection of the routing information may take placethrough comparison of the table update information of the requestingnode with the individual field update information of the fields of therouting tables of the addressed nodes. Such a selection of thetransmitted routing information reduces the data quantity to betransmitted for the routing between the individual nodes. Efficientrouting methods can be implemented in this manner.

[0020] The transmission of the table update information to the addressednodes has the advantage that the table update information requires onlylittle transmission capacity and that only one item of table updateinformation is to be transmitted for each routing table or node. Theupdate request thus occupies only little transmission capacity. This isadvantageous in particular in the case of wireless networks.

[0021] In the advantageous embodiment of the invention as defined inclaim 3, the local routing tables contain a topology change information.The up-to-dateness of a change in the network topology can becharacterized by the topology change information, so that it can beindicated when a change in the network topology has occurred in thenetwork. Preferably, each field in the local routing tables contains anitem of topology change information. This may be, for example, a timeindicator or a sequence number. Since it takes some time until theinformation relating to a change in the network topology has beendistributed over the individual nodes of the network, it can bedistinguished in each node receiving this information later in timewhether this information is new to it, whether it has stored thisinformation already, or whether this information is already obsolete forit, for example because it has already received a more recent item ofinformation from a different node. The topology change information thusrenders it possible to carry out efficient updates of the local routingtables.

[0022] This is achieved in the advantageous embodiment of the inventionas defined in claim 4 in that the update response comprises the topologychange information, and that an update of the individual fields of thelocal routing tables is carried out if the topology change informationof the addressed node is more recent than the topology changeinformation of the requesting node. The node which has sent an updaterequest to adjoining nodes may thus carry out a selective update afterreceiving the replies. An update of the individual fields of therequesting node is carried out if a more up to date or more recentinformation on the network topology is obtained thereby.

[0023] If the topology change information of the addressed node is asrecent as the topology change information of the requesting node,according to the advantageous embodiment of the invention as defined inclaim 7, an update will be carried out if the path length to therespective target node is made shorter by the update.

[0024] In the advantageous embodiment of the invention as defined inclaim 8, an update is carried out if the topology change information ofthe addressed node is as recent as the topology change information ofthe requesting node, and the maximum data transmission rate to therespective target node is made-greater by the update.

[0025] The advantageous embodiments of the invention as defined inclaims 7 and 8 may also be combined, in which case the criterion ofclaim 7 or the criterion of claim 8 may be given a higher priority,depending on the application.

[0026] The embodiment of claim 5 has the advantage that time informationrenders possible an independent comparison of the up-to-dateness of theindividual items of routing information.

[0027] The embodiment having sequence numbers as defined in claim 6 canbe realized in a particularly simple manner.

[0028] It is advantageous in the case of central cluster networks whichhave a central node (controller) for controlling the clusters(sub-networks) to store the routing table for the respective sub-networkcentrally in the central node. The transmission of information betweenthe individual sub-networks takes place via bridge nodes or forwarders.

[0029] The object of the invention relating to the method is achieved bymeans of a method having the characteristics of claim 10.

[0030] A few embodiments of the invention will now be explained in moredetail below with reference to the drawing comprising FIGS. 1 to 6, inwhich:

[0031]FIG. 1 shows a routing table with routing information,

[0032]FIG. 2 shows a dynamic network with 5 sub-networks, eachcontrolled by a central controller, at a first moment in time,

[0033]FIG. 3 shows the network of FIG. 2 at a second moment in time,with a node of the network shifted to an adjoining sub-network ascompared with FIG. 2,

[0034]FIG. 4 is a table showing the time sequence of the change of therouting tables of the central controller as a result of the shift of thenetwork node,

[0035]FIG. 5 shows part of a time register, and

[0036]FIG. 6 shows a network with 5 sub-networks which are eachcontrolled by a central controller.

[0037]FIG. 1 shows a routing table which is stored in the routing nodeor station of a network. The routing table comprises fields T1 to TN foreach station of the overall network as well as a time t_(up) as a tableupdate information, i.e. the time at which the routing table was changedfor the last time. The fields T1 to TN of each individual station of thenetwork comprise 6 sub-fields 1 to 6. The first sub-field 1 contains theidentification number (ID) of the respective target station. The secondsub-field 2 stores the ID of that station to which the data destined forthe target station of the first sub-field 1 are to be passed on. It isthus always stored for each possible target station which is theso-called “next hop” on the way to this target station. If the targetstation itself is the next hop, the target station itself is entered inthe second sub-field 2. The third sub-field 3 stores the generation timet_(gen) of the field as a topology change information. The generationtime t_(gen) indicates when a change has occurred in the networktopology for this field, i.e. for this target station. It is laid downby that station which detects the change in the network topology andsubsequently implements a change in the contents of the field in itslocal routing table. The fourth sub-field 4 contains a time t_(reg).This indicates when a change in the contents of a field was adopted bythe respective station in the routing table owing to a change in thenetwork topology, or when the changes notified by adjoining stationswere adopted. The fifth sub-field 5 of each field contains a quantitysuch as, for example, the remaining path length up to the targetstation. Further quantities may be stored in additional sub-fields ofeach field. The sixth sub-field contains the maximum data rate withwhich data can be transmitted to the target station. This data ratecorresponds to the minimum data rate of all constituent paths from therelevant station to the target station.

[0038] An UPDATE procedure is provided for refreshing the routing tablesso as to keep the routing tables up to date at all times. This UPDATEprocedure is based on a request-response mechanism. Each routing stationperiodically initiates this UPDATE procedure. The station, referred tobelow as the UPDATING station (US), transmits an UPDATE REQUEST messagein the broadcast mode to its immediate (routing) neighbor stations. TheUPDATE REQUEST message contains the time t_(up), i.e. the moment of themost recent table update of the requesting station.

[0039] Upon reception of the UPDATE REQUEST, the neighboring stationscompare the received time t_(up) with the registration times t_(reg) ofeach individual entry in their own routing tables. When this comparisonhas been completed, each neighboring station sends an UPDATE RESPONSEmessage (possibly segmented) to the requesting station US, in whichmessage all those entries of the respective routing table are includedwhich were entered into the table after the moment t_(up), i.e. forwhich it is true that t_(reg)>t_(up). It should be noted that the timet_(up) should generally be converted to the clock system of therespective neighboring station before the times t_(reg) and t_(up) canbe compared. This circumstance and the steps made necessary thereby willbe clarified after the description of the general routing procedure. Allfields are transmitted for each of the entries to be transmitted, exceptfor the next hop terminal ID and the registration time t_(reg), becausethese are irrelevant for the requesting station US.

[0040] Upon reception of the UPDATE RESPONSE, the US compares thegeneration times and quantities of the entries received with thegeneration times and quantities of the entries present at that moment inits own routing table.

[0041] The newly received entries or fields are now denoted “new”, andthe entries of the requesting station obtaining until that moment aredenoted “US”. “PL” denotes the path length, as is apparent in FIG. 1,and “MTR” the maximum transmission rate. MTR^(US-NS) denotes the maximumtransmission rate between the requesting and the replying neighboringstation. By analogy, PL^(US-NS) denotes the number of hops between therequesting station US and the neighboring station NS. This is because itis conceivable that not all stations provide routing data. It could thushappen that two routing stations, which are neighbors in the sense ofthe routing procedure, communicate with one another via one or severalnon-routing stations.

[0042] According to the invention, the US only carries out those entrieswhich fulfill the following criteria: t_(gen)^(new) > t_(gen)^(US)or  (t_(gen)^(new) = t_(gen)^(US)  and  P  L^(new) + PL^(US − NS) < PL^(US))or  (t_(gen)^(new) = t_(gen)^(US)  and  P  L^(new) + PL^(US − NS) = PL^(US)  and  min (MTR^(new), MTR^(US − NS)) > MTR^(US))

[0043] Once the UPDATE criteria for a received entry have beenfulfilled, a few fields of the contents until that moment are replacedas follows:

[0044] the next hop terminal ID is replaced with the ID of the relevantneighboring station.

[0045] the generation time of the new entry is adopted:t_(gen)^(US) = t_(gen)^(new)

[0046] the new path length is: PL^(US)=PL^(new)+PL^(US-NS)

[0047] the new maximum data rate is: MTR^(US)=min(MTR^(new),MTR^(US-NS))

[0048] In this case, too, the station must convert the timet_(gen)^(new)

[0049] into its own time system before time comparisons and replacementscan be carried out (see the explanation further below).

[0050]FIG. 2 shows a network with 5 sub-networks 10 to 14 at a firstmoment t0. The sub-networks 10 to 14 are each controlled by a respectivecentral controller CC1 to CC5. The individual sub-networks 10 to 14 caneach be connected via bridge nodes or forwarders F1 to F5. The bridgenode F1 connects the sub-networks 10 and 11, the bridge node F2 thesub-networks 11 and 12, the bridge node F3 the sub-networks 11 and 13,the bridge node F4 the sub-networks 12 and 14, and the bridge node F5the sub-networks 13 and 14. By way of example, a station ST1 is presentin the sub-network 11. The sub-networks 10 to 14 may comprise furtherstations or nodes (not shown) in any manner whatsoever. In addition,FIG. 2 shows the transmission rates of the links between the individualsub-networks as well as between the CC2 and the station ST1. Thetransmission rate between the sub-network 10 and the sub-network 11 viathe forwarder F1 is 10 Mbit/s, the transmission rate between thesub-network 11 and the sub-network 12 via the forwarder F2 is 5 Mbit/s,the transmission rate between the sub-network 11 and the sub-network 13via the forwarder F3 is 0.1 Mbit/s, the transmission rate between thesub-network 12 and the sub-network 14 via the forwarder F4 is 1 Mbit/s,and the transmission rate between the sub-network 13 and the sub-network14 via the forwarder F5 is 3 Mbit/s. Finally, the transmission ratebetween the controller CC2 and the station ST1 is 5 Mbit/s. The links inthe network shown by way of example in FIG. 2 thus always pass throughthe central controllers CC1 to CC5.

[0051]FIG. 3 shows the network with 5 sub-networks of FIG. 1 at a secondmoment t1. The topology of the network has changed at this secondmoment, i.e. the station ST1 has moved from the sub-network 11 to theneighboring sub-network 10. 1The transmission rate between thecontroller CC1 of the sub-network 10 and the station ST1 now is 10Mbits/s.

[0052]FIG. 4 illustrates the changes in the routing tables of thecontrollers CC1 to CC5 over time as a result of the shift of the stationST1 from the sub-network 11 of FIG. 2 to the sub-network 10 as shown inFIG. 3.

[0053] The Table of FIG. 4 contains a column for each of the controllersCC1 to CC5. The fields of the routing tables of the individualcontrollers for the target station ST are indicated in the columns atfive different moments t0 to t4 for the controllers CC1 to CC5. Thefields in this example each have 5 sub-fields. The sub-field provided inaccordance with FIG. 1 containing the identification number (ID) of therespective target station is not shown in FIG. 4, because FIG. 4 showsrouting information relating to the target station ST1 only.

[0054] The upper sub-field of the fields in FIG. 4 indicates the bridgenode or forwarder to which the data destined for the station ST1 are tobe passed on. This means that only the so-called next hop on the way tothis target station ST1 is stored each time for this target station ST1.The second sub-field 5 from the top contains the remaining path lengthup to the target station. The central sub-field contains the maximumdata rate with which data can be transmitted to the target station ST1.This data rate corresponds to the minimum data rate of all constituentpaths from the relevant controller up to the target station ST1. Thesecond sub-field from the bottom provides the generation time t_(gen) ofthe field for the target station ST1 by way of topology changeinformation. The generation time t_(gen) indicates when a change hasoccurred in the network topology for the target station ST1. It isregistered by that station which detects the change in the networktopology and subsequently carries out a change in the contents of thefield in the local routing table. In the present case this is thecontroller CC1 of the sub-network 10. The bottom sub-field contains thetime t_(reg). This indicates when the change in the network topology wasincluded into the respective routing table by the respective station,i.e. in this example by the respective controllers, or when the changestransmitted by neighboring stations were adopted.

[0055] In the present example, the column contains the fields of therouting tables of the controllers CC1 to CC5 for the target station ST1and the network in accordance with FIG. 2 at the moment t0.

[0056] At the moment t1, the target station ST1 is shifted from thesub-network 11 to the sub-network 10. This corresponds to the networktopology of FIG. 3. This is recognized by the controller CC1 of thesub-network 10, and this controller CC1 accordingly changes its routingtable at the moment t1. The topology change information has accordinglyarisen at the moment t1, which means that t_(gen)=1 is set. The changethat has occurred in the network topology was also entered by thecontroller CC1 in its routing table at the moment t1 and registeredaccordingly. This means that t_(reg) is also set for 1. The controllersCC2 to CC5 do not know the change in the network topology at the momentt1 yet. This information must first be distributed over the network.This is done by means of the requests sent by the individual controllersto the neighboring controllers at regular intervals, and by means of therelevant responses of the controllers thus addressed.

[0057] The controller CC2 receives a reply to its request from thecontroller CC1 at the moment t2, and the change in the network topologyis entered into the routing table of CC2. Since the topology change hasoccurred at the moment t1, t_(gen)=1 is set. The change in the networktopology was entered by the controller CC2 into its routing table at themoment t2 and registered accordingly. This means that t_(reg) is set for2.

[0058] The controllers CC3 and CC4 receive a reply to their requestsfrom the controller CC2 at the moment t3, and the change in the networktopology is entered into the routing tables of CC3 and CC4. Since thetopology change has occurred at the moment t1, t_(gen)=1 is set. Thechange in the network topology was entered into the routing tables bythe controllers CC3 and CC4 at the moment t3 and registered accordingly.This means that t_(reg) is set for 3.

[0059] The controller CC5 receives a reply to its request from thecontroller CC3 and/or the controller CC4 at moment t4, and the change inthe network topology is entered into the routing table of CC5. Since thetopology change has occurred at the moment t1, t_(gen)=1 is set. Thechange in network topology was entered into the routing table of therespective controller CC5 at the moment t4 and registered accordingly.This means that t_(reg) is set for 4.

[0060] The further sub-fields are also adapted to the changed networktopology at the respective moments t1 to t4 in a corresponding manner.

[0061] Additional functions may be implemented in the routing, if sodesired. The constant period of refreshing of the routing tables meansthat topology changes occurring between two UPDATE moments are notcommunicated immediately to the neighboring stations, but at the nextUPDATE moment. Advantageously, however, particularly important changes,such as the failure of connection paths, may also be communicated to theneighbors without any preceding request. This is done by means of anUPDATE TRIGGER message which contains the relevant entries relating tothe changed fields.

[0062] To avoid data on current links being lost in the time between thetopology change and the next UPDATE moment, moreover, the node detectingthe topology change may send an ERROR message to the sources or endterminals of the relevant links in order to stop the current connection.

[0063] The moments in time t_(up), t_(gen), and t_(reg) defined in theprotocol may be coded in various ways. An obvious coding relates to anoverall system clock which is coded as a multiple of a basic clockmodulo a maximum value in the form of a bit sequence. The use of anoverall system clock, however, would require a synchronization of allstations of the network. Some communication standards (for example thestandard 1394.1) already achieve a synchronization of all appliances ofa network, but the availability of an overall system clock cannot betaken for granted in general.

[0064] For this reason, the use of an overall system clock is avoided.The algorithm is in fact already fully functional if neighboringstations are informed about the difference between their local times orclocks. It is accordingly provided that neighboring stations inform oneanother of their prevailing local system clocks. The period of thisinformation exchange may usually be chosen to be extremely wide, as willbe explained further below. The clock information exchange thusrepresents a negligibly small occupation of transmission resources. Eachstation stores the difference between its local time and the local timeof each individual neighboring station. When a station receives anUPDATE request with the parameter t_(up), it will add the clockdifference stored in relation to the relevant neighboring station tot_(up) so as to convert the moment of the most recent change in therouting table of the neighboring station into its own time system. Thenthe converted time t_(up) may be compared with the registration timest_(reg) of the own routing inputs in accordance with the normal routingprocedure, and an UPDATE response can be generated. When a stationreceives an UPDATE response to a preceding UPDATE request, thegeneration time t_(gen) of each entry received is first converted intothe local time system exactly as in the preceding case in that the clockdifference with the relevant neighboring station is added to the timet_(gen). Then it is decided in accordance with the normal run of therouting algorithm whether the received entry is to be included into theown routing table or not.

[0065] It should be noted that the clock difference stored by twoneighboring stations has opposed signs, i.e. in the case of an exchangeof an UPDATE request and UPDATE response between two neighboringstations the addition of a positive clock difference value in onestation will correspond to the subtraction of the same positive value(i.e. the addition of a negative value) in the other station.

[0066] Clock generators usual at present generally have an accuracy inthe microsecond or nanosecond range. Such a high accuracy of the timedefinition is not necessary for the routing procedure under discussionhere. To minimize the number of bits to be transmitted, accordingly, nomore than a fraction of the internal clocks of the stations is used forthe time indicators t_(up), t_(gen), and t_(reg).

[0067]FIG. 5 shows by way of example an excerpt from a complete timeregister. The intervals of the register shown in FIG. 5 correspond tosingle bits. The time value is dually coded, the significance of thebits increasing from right to left, so that the Most Significant Bit(MSB) lies at the extreme left.

[0068] The excerpt of the register chosen for the routing procedure,shown hatched in FIG. 5, is determined by the two times T_(max) andT_(min).

[0069] The upper limit of the chosen register excerpt determines themaximum time after which an entry into a routing table must be erased.This is based on the modulo definition of the time excerpt within therouting procedure. A station must test each entry already present in therouting table at each time step (T_(precision)) as to whether thegeneration time t_(gen) of the entry corresponds to the current localtime (or the excerpt from the time register). If this is the case, theentry is erased. This is because an old entry would otherwise seem to behighly up to date again after one modulo period because of the modulodefinition.

[0070] The order of magnitude of T_(min) determines the accuracy of thetime coding and bases itself on the minimum period of transmission ofthe UPDATE request messages. The reason for this is that all entrieschanged in the responding station since the latest UPDATE of therequesting station are sent to the requesting station, independently ofwhether the changes were implemented shortly or long after the latestUPDATE. The same holds for the replacement of entries in the requestingstation. A more accurate coding of the time will give no advantage inthis respect and will merely occupy transmission capacity.

[0071] Advantageously, however, an excerpt enlarged by a few bits indownward direction (up to the time T_(precision) in FIG. 5) is chosenfor transmitting and storing the times t_(up), t_(gen), and t_(reg),although only the bits fully hatched in FIG. 5 are actually processed inthe routing algorithm. Propagation effects of rounding errors in theconversion of the clocks of one timing system into another timing systemcan be avoided in this manner.

[0072] The register excerpt is laid down once and for all and cannot bechanged during the operation of individual stations.

[0073] The same is not true, however, for the period of transmission ofthe UPDATE request messages. The routing method does not require allstations to use the same period. This is utilized in the sense that eachstation optimizes its own UPDATE period during operation. Empty UPDATEresponse messages may, for example, point to the fact that the UPDATEperiod can be expanded. High topology change rates and subsequentconnection interruptions and packet losses should lead to a reduction ofthe UPDATE period. The routing method thus automatically adapts itselfto various system scenarios and mobility rates.

[0074] In accordance with the coding instruction shown, the statementmade initially may now be motivated, i.e. the statement that theinformation exchange for determining the clock differences betweenneighboring stations may take place comparatively seldom: the frequencyof the information exchange follows the so-termed clock drift of thelocal clock generator of each station. Usually the clock drift is of theorder of or even a few orders of magnitude lower than the minimum codinglevel of the clock register (least significant bit or LSB in FIG. 5).The lower limit of the excerpt considered, i.e. the time T_(min),however, is chosen to be higher by a few powers of two as shown in FIG.5. An exchange of information on the clock differences should then takeplace at the latest when a shift of the order of T_(precision) could beachieved on account of the clock drift.

[0075] Subsequently, the exchange of information about the clockdifferences is represented for a self-organizing network organized inthe form of sub-networks or clusters. An example of such a network isshown in FIG. 6.

[0076] In the cluster-based network of FIG. 6, a single station, thecentral controller (CC), carries out the routing algorithm for allstations of its own cluster. The network of FIG. 6 comprises fiveclusters 20 to 24. The clusters 20 to 24 have CCs 30 to 34. This meansthat only the CCs 30 to 34 are neighbors in the sense of the routingmethod described above. The CCs, however, cannot communicate directlywith one another in general, but they must exchange information viaso-termed forwarding terminals (FT) which lie in the overlapping regionsof the clusters. The clusters 20 and 22 are connected by means of an FT40, the clusters 21 and 22 by means of an FT 41, the clusters 22 and 23by means of an FT 42, and the clusters 24 and 22 by means of an FT 43.The cluster 20 has, for example, a further station 50, the cluster 21further stations 51 and 52, the cluster 23 further stations 53 and 54,and the cluster 24 further stations 55 to 57.

[0077] The time or clock information is exchanged between the CCs 20 to24 in the following manner: each FT 40 to 43 and each CC 20 to 24 storesa copy of its complete clock register at the start of each MAC frame.Furthermore, each CC periodically (in accordance with the period of theclock information exchange) transmits a broadcast message within itscluster in which the copy of the clock register at the start moment ofthe present MAC frame is contained as a parameter. The FTs receivingthis message form the difference from the copy of their own clockregister and the received copy of the clock register of the CC. In thismanner they determine the shift between the clocks of the CC and theirown clocks and store this difference. Once an FT has determined thedifference with a further CC by the same procedure, it is capable ofdetermining the clock difference of the two CCs by subtracting the twoshift values. The clock difference is subsequently transmitted to thetwo CCs in a signaling message specially designed for this purpose.

1. A dynamic network with a plurality of nodes, in which it is providedthat routing information is stored in local routing tables in nodes ofthe network, the nodes send an update request to other nodes forupdating the local routing tables, and the addressed nodes send anupdate response with updating routing information to the requestingnodes.
 2. A network as claimed in claim 1, characterized in that thetables comprise fields for the target nodes, in that the local routingtables contain a table update information relating to the most recentupdating of the local routing table and a field update informationrelating to the most recent updating of the individual fields, in thatthe update request contains the table update information, and in thatthe update response contains those items of local routing informationfor which the field update information of the addressed node is more upto date than the table update information of the requesting node.
 3. Anetwork as claimed in claim 1, characterized in that the local routingtables contain fields for the target nodes, and in that the fieldscontain a topology change information for characterizing theup-to-dateness of a change in the network topology.
 4. A network asclaimed in claim 3, characterized in that the update response containsthe topology change information, and in that the requesting node afterreceiving the update responses from the addressed nodes carries out anupdate of its local routing table if the topology change information ofthe addressed node is more up to date than the topology changeinformation of the requesting node.
 5. A network as claimed in claim 1,characterized in that the table update information and/or the fieldupdate information and/or the topology change information are items oftime information.
 6. A network as claimed in claim 1, characterized inthat the table update information and/or the field update informationand/or the topology change information is/are constituted by sequencenumbers.
 7. A network as claimed in claim 1, characterized in that therequesting node after receiving the update responses from the addressednodes carries out an update of its local routing table if the topologychange information of the addressed node is equally up to date as thetopology change information of the requesting node and the path lengthto the respective target node is made shorter by the update.
 8. Anetwork as claimed in claim 1, characterized in that the requesting nodeafter receiving the update responses from the addressed nodes carriesout an update of its local routing table if the topology changeinformation of the addressed node is equally up to date as the topologychange information of the requesting node and the maximum datatransmission rate to the envisaged target node is made higher by theupdate.
 9. A network as claimed in claim 1, characterized in that thenetwork can be subdivided into several sub-networks which each contain acontroller for controlling the sub-networks, in that the sub-networkscan be interconnected by means of respective forwarding terminals, andin that each controller is designed for storing and managing a centralrouting table for the respective sub-network.
 10. A routing method for adynamic network comprising a plurality of nodes, wherein it is providedthat routing information is stored in local routing tables in nodes ofthe network, the nodes send an update request to other nodes forupdating the local routing tables, and the addressed nodes send anupdate response with updated routing information to the requestingnodes.
 11. A node for a dynamic network, in which it is provided thatrouting information is stored in a local routing table, the node sendsan update request to other nodes for updating the local routing table,and the node sends an update response with updated routing informationto other requesting nodes.